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Life Sciences Contribution Q7 
Royal Ontario Museum vy / 

A Revision of the Longipinnate 
Ichthyosaurs of the Lower Jurassic 
of England, with Descriptions of 
Two New Species 
(Reptilia: Ichthyosauria) 

C. McGowan 



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Digitized by the Internet Arcliive 

in 2011 witii funding from 

University of Toronto 



littp://www.archive.org/details/revisionoflongipOOmcgo 



LIFE SCIENCES CONTRIBUTIONS 
ROYAL ONTARIO MUSEUM 
NUMBER 97 



c. McGowAN A Revision of the Longipinnate 

Ichthyosaurs of the Lower Jurassic 
of England, with Descriptions of 
Two New Species 
(Reptilia: Ichthyosauria) 



Publication date: 29 April 1974 

ISBN 0-88854-151-1 

Suggested citation: Life Sci. Contr., R. Ont. Mus. 



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CHRISTOPHER MCGOWAN is Assistant Curator, Department of Vertebrate Palaeontology, 
Royal Ontario Museum, and Assistant Professor, Department of Zoology, University 
of Toronto. 



price: $1.50 

© The Royal Ontario Museum, 1974 

100 Queen's Park, Toronto, Canada 

printed AT the BRYANT PRESS LIMITED 



A Revision of the Longipinnate 
Ichthyosaurs of the Lower Jurassic of 
England, with Descriptions of Two 
New Species (Reptilia: Ichthyosauria) 



Abstract 

A revision of the longipinnate ichthyosaurs of the English Lias 
(Lower Jurassic) estabhshes five valid species. One of these 
is referred to the Upper Liassic genus Stenopterygius, the 
others to the genus Temnodontosaurus Lydekker, 1889, which 
is predominantly Lower Liassic in age. Two new Lower Liassic 
species are described. A detailed account of the variates meas- 
ured is given. 

Zusammenfaasung 

Eine Revision der longipinnaten Ichthyosaurier des englischen 
Lias (Untere Jura) stellt fuenf gueltige Arten auf. Eine von 
diesen bezieht sich auf die aus dem oberen Lias stammende 
Gattung Stenopterygius, die anderen auf die Gattung Temno- 
dontosaurus Lydekker, 1889, welche ueberwiegend aus dem 
unteren Lias stammt. Ein ausfuehrhcher Bericht ueber die 
gemmessenen Verschiedenheiten wird gegeben. 



Introduction 

The Lower Jurassic deposits of England are well endowed with the remains 
of ichthyosaurs, which have been collected intensively since the beginning 
of the last century. Most material came from the Lower Lias [Hettangian and 
Sinemurian], the principal locaHties being Lyme Regis, Dorsetshire; Street, 
in the adjoining county of Somersetshire; and Barrow-on-Soar, Leicester- 
shire. Ichthyosaurs are also known from the Upper Lias [Lower Toarcian], 
but this horizon has so far yielded only longipinnates. The principal Upper 
Liassic locality is the Whitby district of Yorkshire, equivalent in age to the 
famous Holzmaden locality of Germany. Longipinnates are also found in the 
Lower Lias but are less numerous than latipinnates. The distinction between 
latipinnates and longipinnates is discussed in detail elsewhere (McGowan, 
1972a), the major differences occurring in the forefins; longipinnates have 
three distal carpals hence three primary digits, whereas latipinnates have 
four distal carpals thus four primary digits. 

A recent review of the Lower Liassic latipinnates (McGowan, in press) 
showed the systematics to be confused, two thirds of the species being 
invalid. Similar confusion occurs in the longipinnates and the problem is 



complicated by the question of the generic name. The Liassic latipinnates 
belong to the genus Ichthyosaurus De La Beche and Conybeare, 1821, but 
the appropriate name for the Liassic longipinnates is problematic. Charig 
(in preparation) has made a detailed study of the nomenclatural status of 
the English Liassic ichthyosaurs. He notes that as Temnodontosaurus 
Lydekker, 1889 (in Nicholson and Lydekker, 1889) has /. platyodon 
Conybeare, 1822, as its type-species, Temnodontosaurus is available as the 
generic name for that taxon. My study shows /. platyodon to be one of a 
group of four species referable to a single genus, and Temnodontosaurus 
thus has priority as the generic name for these longipinnates. 

As many as eight longipinnate species have been described from the 
English Lias (see Lydekker, 1889a; Von Huene, 1922) and these will be 
referred, for the present, to their original genus. Ichthyosaurus: I. acuti- 
rostris Owen, 1840; /. crassimanus Blake, 1876; /. latifrons Koenig, 1825; 
/. lonchiodon Owen, 1840; /. longifrons Owen, 1881; /. longirostris Man- 
tell, 1851; / platyodon Conybeare, 1822; and /. zetlandicus Seeley, 1880. 
The purpose of this paper is to clarify the systematics of these English 
longipinnates. 



Materials and Methods 



Materials 

Measurements were taken directly from 20 specimens and from photo- 
graphs of an additional four specimens. Of these, 13 were from the Lower 
Lias [Hettangian and Sinemurian] of Lyme Regis, Street, and Barrow-on- 
Soar, and 1 1 from the Upper Lias [Lower Toarcian] of Whitby. The 
abbreviations used for collections examined are: bmnh, British Museum 
(Natural History), London; lcm, Leicester County Museum, England; 
OUM, Oxford University Museum; ROM, Royal Ontario Museum, Toronto; 
sec. Street Collection, in the care of Clarks Shoe Company, Street, Somer- 
set; SMC, Sedgwick Museum, Cambridge University; uw. University of 
Wyoming; wmy, Whitby Museum, Yorkshire; and ym, York Museum, 
Yorkshire. 



Methods 

All measurements were made with 
vernier calipers accurate to .01 cm, 
except those of body length which 
were made with a tape accurate to 
0.1 cm. Because of incomplete pres- 
ervation or exposure of bony ele- 
ments (the term indeterminate is 
used in this context in the sections 
which follow) few post-cranial char- 
acters were used, viz: length of 
body, vertebral count to pelvic gir- 
dle, vertebral count to tail bend, 
length of forefin, width of forefin, 
total digital count, number of pri- 
mary digits, number of accessory 
digits, number of elements in long- 
est digit, and occurrence of notching 
(Fig.l). 

The cranial measurements re- 
corded are shown in Fig. 2. Because 
of size variation it was necessary to 
convert all continuous variates into 
ratios, and those derived from cran- 
ial measurements are: diameter of 
orbit (3) to length of jaw (7), 
length of snout (6) to length of jaw 
(7), length of premaxillary segment 
(1 ) to length of jaw (7), length of 



notches 



width- 








.®qO' 



WHO 

OC®oo 



c 





t (^ p-4 * 

accessory 

digit 



primary 
digits 

Fig. 1 Diagram of a longipinnate forefin 
(left, dorsal view) showing the 
distinction between primary and 
accessory digits. The maximum 
number of elements in the longest 
digit is 12. 



B 




Fig. 2 Diagram of an ichthyosaur skull showing the cranial measurements: 

1, length of premaxillary segment; 2, length of external naris; 3, diameter of 
orbit; 4, internal diameter of sclerotic ring; 5, length of prenarial segment; 
6, length of snout; 7, length of jaw. 

A-A, longitudinal axis of orbit; B-B, longitudinal axis of skull; Ang, angular; 
Dent, dentary; Quad, quadrate; Sur, surangular; Max, maxilla. 



prenarial segment (5) to length of jaw (7), length of external naris (2) to 
diameter of orbit (3), internal diameter of sclerotic ring (4) to diameter of 
orbit ( 3 ) . Due to small sample sizes and missing data a statistical analysis was 
not possible. It is therefore not known whether the ratios are affected by 
allometric growth, nor whether they are normally distributed. However, 
I have found intercranial growth (relative to jaw length) to be almost 
completely isometric in Stenopterygius quadriscissus, Ichthyosaurus com- 
munis and /. breviceps (McGowan, 1973a) and this might also hold for 
the present species. Furthermore an analysis of data for /. communis and 
/. breviceps (McGowan, in press) and S. quadriscissus (McGowan, in 
preparation) has shown all ratios to be normally distributed. 



Details of Yariates Recorded 

AXIAL SKELETON 

Length of body, the length, measured along the vertebral column, 
from first to last vertebra. 

Vertebral count to the pelvic girdle: the number of vertebrae 
counted from the adas to the position of the pelvic girdle. The atlas is 
quite distinct because it is fused with the axis (Fig. 3a). The position of 
the pelvic girdle is taken as that centrum which lies closest to the vertical 
level of the ilium. The pelvic girdle is frequendy displaced or lost and in 
this case an estimate is made based upon the position of the proximal 
head of the femur. 

Vertebral count to the tail bend: the number of vertebrae counted 
from the atlas to the apex of the tail bend. Where the tail bend is distinct 
there is little difficulty in making the count which is condnued up to, and 
includes, that centrum at the apex of the bend. The apical centra are 




B 





'^ 



Ly 



LJ 



r^ 




QOOOQQOOOOOOOOO 



constriction 



Fig. 3 Features of the ichthyosaurian vertebral column, scale = 10 cm. 

A. Anterior portion of vertebral column of Ichthyosaurus communis. Lower Lias, 
Lyme Regis; A, atlas centrum; B, axis centrum; C, centrum of third cervical 
vertebra; D, neural arch of atlas; E, neural arch of axis; F, fused neural spine 
of atlas and axis; G, neural spine of third vertebra; H, neural arch of third 
vertebra. 

B. Tail bend region of Ichthyosaurus communis (bmnh 2013), Lower Lias, 
Lyme Regis. Note the wedge-shaped centra at the apex of the bend. 

c. Diagrammatic representation of the tail bend region in a dorso-ventrally 
preserved specimen showing how the rate of decrease in diameter of the centra 
is reduced distal to the apex of the bend. 



wedge-shaped, widest dorsally, and these clearly mark the apex of the tail 
bend (Fig. 3b). Where the bend is indistinct, as in dorso-ventrally com- 
pressed specimens, its position can often be estimated by considering the 
rate of taper in the diameter of the centra. The gradual decrease in diam- 
eter towards the tip of the tail is less marked in those centra lying distal 
to the tail bend than in those proximal to the tail bend. Consequently 
there is a slight constriction at this level (Fig. 3c). When a constriction 
is not apparent its position can often be revealed by measuring the diam- 
eters of the centra, a marked difference in the diameters of adjacent centra 
indicating the position of the tail bend. 

SKULL (see Fig. 2) 

Length of skull: the distance between the tip of the snout and the 
posterior edge of the articular surface of the quadrate. The quadrate is 
selected as a point of reference because it has no contact with post-cranial 
structures and is therefore usually well defined. Occasionally the quadrate 
is displaced, in which case allowances must be made. 

Length of snout: the distance between the tip of the snout and the 
anterior boundary of the orbit. Von Huene (1922) measured to the 
anterior boundary of the external narial opening, but the boundaries of the 
naris are often indeterminate. 

Length of prenarial segment: the distance between the tip of the 
snout and the anterior boundary of the external naris. Occasionally the 
bones surrounding the narial aperture are pushed inwards, forming a trian- 
gular depression, and this may be misinterpreted as the external naris. As a 
general guide the anterior boundary of the external naris is rounded, 
whereas depressions tend to be angular. 

Length of premaxillary segment: the distance between the tip of 
the snout and the anterior tip of the maxilla. The free margin of the maxilla 
forms a continuous straight edge with that of the premaxilla, and a break in 
continuity in this region is indicative of damage or displacement of the 
maxilla. Where such damage has occurred an approximation can be made 
by projecting the maxillary margin forward until it intersects with the 
premaxilla. 

Longitudinal diameter of orbit: the maximum internal diameter of 
the orbit. The orbit is oval rather than round, and its longitudinal axis 
may not necessarily correspond with the longitudinal axis of the skull (an 
axis passing through the tip of the snout and the articular surface of the 
quadrate). The longitudinal diameter of the orbit is measured along the 
orbital axis, at the widest point. The posterior boundary of the orbit is 
invariably well defined and is the anterior surface of the postorbital. The 
anterior boundary is the internal (posterior-facing) surface of the lachry- 
mal. Sometimes the lachrymal bears a posterior projection of bone which 
has the appearance of a crescentic swelling in the antero-dorsal corner of 
the orbit and which interferes with the measurement. However, by pro- 
jecting the line of the orbit (i.e., the curvature of the jugal) forward, it 
is possible to estimate the anterior boundary of the orbit. 



Internal diameter of sclerotic ring: the maximum internal diam- 
eter of the sclerotic ring. The aperture of the sclerotic ring is usually oval, 
and the maximum internal diameter lies approximately parallel to the 
longitudinal axis of the orbit. If distortion has occurred and the maximum 
diameter lies perpendicular to the longitudinal axis of the orbit, or if the 
aperture is asymmetric, a correction must be made. In both instances the 
internal diameter is taken as the mean of the maximum diameter, and the 
diameter measured at right angles to it. 

Length of external naris: the distance between anterior and pos- 
terior boundaries of the external naris measured between verticals. 

LOWER JAW^ 

Length of jaw: the distance between the anterior tip of the dentary 
and the posterior edge of the surangular, measured between verticals 
perpendicular to the longitudinal axis of the skull. 

DENTITION 

Form of teeth : the teeth lie with their bases in a dentigerous groove 
and for this reason are seldom seen in their entirety. Note is taken of the 
tooth shape. 

Number of maxillary teeth: the number of teeth in the upper jaw 
counted from the most posterior tooth, to that at the anterior tip of the 
maxilla. The most anterior maxillary tooth may lie partly in contact with 
the premaxilla, but provided it maintains contact with the maxilla it is 
counted as a maxillary tooth. 

FINS (see Fig. 1 ) 

Length of fore- and hindfin: the distance between the distal end of 
the propodial and the most distal phalanx, measured between horizontals 
perpendicular to the longitudinal axis of the fin. The propodial is not 
included in the length of the fin because of the difficulty in accurately deter- 
mining its length. The terminal phalanges are usually very small and often 
well spaced so that they do not make contact with one another. Sometimes 
they are obscured by matrix, or lost altogether, but if the most distal 
phalanges are relatively small it may be assumed that the fin is complete. 

Width of fore- and hindfin : the maximum width measured between 
verticals parallel to the longitudinal axis of the fin. 

Number of primary digits: the maximum number of primary digits. 

Total digital count: the total number of primary and accessory 
digits. Accessory digits frequendy contain only a few elements, but if they 
exceed three in number they are counted. 

Occurrence of notching in fin elements: notches are often obscured 
by matrix, which it is sometimes necessary to remove. 

Number of elements in longest digit: numerically equal to the 
horizontal level of the most distal fin element. The count commences at 
the level of the epipodials (level one). 



Estimates of Growth Constants a and b 

Estimates of the allometric growth constants a and b for the growth of 
the head relative to the body were evaluated using the logarithmic trans- 
formation of the allometric growth equation y = bx" (where y = organ 
size and x = body size). Bartlett's Model ii regression technique was used 
in the computation, but the small sample size did not permit confidence 
limits to be set for the estimates of a and b (for details of the method see 
McGowan, 1973a). 



8 



Systematic Descriptions 



I find that only three of the eight previously described English longipinnate 
species from the Lower Jurassic are valid; /. platyodon Conybeare, 7. 
acutirostris Owen and 7. longirostris Mantell. To these three are added 
two new species (described below), both from the Lower Lias of Lyme 
Regis, Dorset. 7. crassimanus Blake, 7. longifrons Owen and 7. zetlandicus 
Seeley are all junior synonyms for 7. acutirostris; I. lonchiodon Owen is a 
junior synonym for 7. platyodon, and 7. latlfrons Koenig is rejected as a 
nomen dublum. 

I. acutirostris (Upper Lias, Yorkshire) has closer affinity with the Ger- 
man species Stenopteryglus quadrlsclssus (Quenstedt) (Upper Lias) than 
with the other English longipinnates, and is accordingly referred to the 
genus Stenopteryglus. The remaining four English species are referred to 
the genus Temnodontosaurus Lydekker ( 1 889b, pp. xi, 1 126) . 



Class Reptilia 

Subclass £uryapsida(?) 

Order Ichthyosauria 

Suborder Longipinnati Von Huene, 1948 



Family Temnodontosauridae fam. nov. 

Diagnosis 

Forefin with no more than three primary digits, one of which supported 
by intermedium; total digital count probably does not exceed four; orbit 
relatively small, ratio, diameter of orbit to length of jaw ^ 0.21; aperture 
of sclerotic ring to diameter of orbit probably always < 0.35; maxilla 
relatively long, ratio, length of premaxillary segment to length of jaw 
^ 0.40; external naris frequently relatively long, ratio, length of external 
naris to diameter of orbit often > 0.45; moderate to very large, adult jaw 
length ^ 60 cm and usually > 100 cm. Liassic in age and predominantly 
from the Lower division. 



Type genus Temnodontosaurus Lydekker 1889b 

Diagnosis 

As for the Family Temnodontosauridae 

Type species 

Temnodontosaurus platyodon (Conybeare) 




Q 



O 



m 



Fig. 4 Temnodontosaunis platyodon (Conybeare), scale = 25 cm. 

A. BMNH 2003, dorsal view, Lower Lias, Lyme Regis; b. bmnh R1158, Lower 
Lias, Lyme Regis; c. bmnh 2003, left forefin, dorsal view; d. gum J29170, right 
forefin, ventral view, Lower Lias, Lyme Regis. 



10 



Temnodontosauriis platyodon (Conybeare) 

Fig. 4 

Ichthyosaurus platyodon Conybeare, 1822, p. 108, pi. 15, fig. 7; pi. 16, 

figs. 1-7. 

Ichthyosaurus platyodon Conybeare, De La Beche, 1826, p. 27. 

Ichthyosaurus chiroligostinus Hawkins, 1834, p. 14, pi. 3. 

Ichthyosaurus chiroligostinus Hawkins, Hawkins, 1840, p. 10, pi. 2, pi. 3. 

Ichthyosaurus platyodon Conybeare, Owen, 1840, p. 112. 

Ichthyosaurus lonchiodon Owen, 1840, p. 116. 

Ichthyosaurus platyodon Conybeare, Mantell, 1851, p. 380. 

Ichthyosaurus lonchiodon Owen, Mantell, 1851, p. 384. 

Ichthyosaurus platyodon Conybeare, Owen, 1881, p. 115, pi. 24, fig. 4; 

pi. 31, figs. 1-3. 

Ichthyosaurus lonchiodon Owen, Owen, 1881, p. 117, pi. 24, fig. 6; pi. 31, 

figs. 4-7. 

Ichthyosaurus platyodon Conybeare, Lydekker, 1889a, p. 94, fig. 34. 

Ichthyosaurus lonchiodon Owen, Lydekker, 1889a, p. 92. 

Temnodontosaurus platyodon (Conybeare), Lydekker, 1889b, p. xi. 

Leptopterygius platyodon (Conybeare), Von Huene, 1922, p. 18, pi. 2, 

fig. 2; pi. 3, fig. 3. 

Leptopterygius lonchiodon (Owen), Von Huene, 1922, p. 16, pi. 3, fig. 1. 

Leptopterygius (Ichthyosaurus) platyodon (Conybeare), Delair, 1969, p. 10. 

Leptopterygius platyodon (Conybeare), Delair, 1969, p. 11. 

Proteosaurus platyodon (Conybeare), McGowan, 1972a, p. 5, fig. 2b. 

Proteosaurus platyodon (Conybeare), McGowan, 1972b, p. 5, figs. 9, 11. 

Emended Diagnosis 

Very large ichthyosaurs, length of jaw > 100 cm, and > 150 cm in mature 
individuals; snout relatively long and straight, ratio, length of snout to 
length of jaw ^ 0.62; skull and lower jaw with rectilinear profile; orbit 
relatively small, ratio, diameter of orbit to length of jaw not exceeding 0.18 
and probably always < 0.18; sclerotic aperture relatively small, ratio, 
internal diameter of sclerotic ring to diameter of orbit < 0.35; maxilla 
relatively long, ratio, length of premaxillary segment to length of jaw 
< 0.36; external naris relatively long, ratio, length of external naris to 
diameter of orbit usually > 0.60; ratio, length of prenarial segment to 
length of jaw > 0.42; forefin long and narrow with three primary digits 
and probably one post-axial accessory digit; maximum number of elements 
in longest digit does not exceed 18; radius and radiale notched, possibly 
other elements too. Lower Liassic in age [Upper Hettangian to Lower 
Sinemurian] and largely, if not wholly, confined to Lyme Regis, Dorset- 
shire. 

Original type material 

A single tooth was figured in the original description of the species /. platy- 
odon (Conybeare, 1822, pi. 15, fig. 7), which was in the care of the Geolog- 

II 



ical Society of London (Woodward and Sherborn, 1890, p. 240). A search 
for this tooth was unsuccessful (Delair, 1960). 

Proposed Neotype 

BMNH 2003, a complete skeleton in the British Museum (Natural History). 

Evidence that proposed neotype is consistent with what is known of original 
type material 

Conybeare's original description of /. platyodon made reference to the large 
size, "the most gigantic yet discovered" (1822, p. 108). The proposed neo- 
type, BMNH 2003, with a total length of 6.38 metres, is one of the largest 
Lower Liassic specimens, and is therefore consistent with Conybeare's 
original description. 

Evidence that proposed neotype came as nearly as practicable from original 

type-locality 

Conybeare did not specify the type-locality but did note that the species 

occurred in the Lias (1822, p. 108). At that time most ichthyosaurian 

material was being collected from Lyme Regis, and to a lesser extent from 

Somerset. As both of these locaHties are Lower Liassic, it may be inferred 

that the material was Lower Liassic in age. 

Other material 

BMNH R2918, BMNH 14564 (complete skeletons); oum J29170 (incom- 
plete skeleton); bmnh R1158, bmnh R1155, bmnh R215 (complete or 
near complete skulls) and rom 7972 (partial skull). 

Locality and Horizon 

All material thus far referred to this species is from the Lower Lias of 
Lyme Regis, Dorset. De La Beche (1822) noted that remains of ichthy- 
osaurs were "by no means rare" and were principally discovered at Black 
Ven, most commonly in the slaty or marly part of the Lias. The lowest 
horizon exposed at the foot of Black Ven is that of Arnioceras semi- 
costatum (Fig. 5). In a later paper De La Beche (1826) recorded that 
the Liassic limestones of Lyme Regis contain numerous organic remains, 
including ichthyosaurs, which are found principally in the marls alternating 
with limestones containing the ammonite, Arietites bucklandi (i.e., the top 
of the Blue Lias). Most of the material from Lyme Regis was probably 
collected from the Blue Lias, from the zones of Arietites bucklandi and 
Arnioceras semicostatum (see Arkell, 1933). While it is possible that ich- 
thyosaurs have been collected from higher zones, the geological range of 
specimens from Lyme Regis will be taken to be from the zone of Schlo- 
theimia angulata to that of Arnioceras semicostatum [Upper Hettangian- 
Lower Sinemurian]. 

Emended Description 

Temnodontosaurus platyodon is one of the largest ichthyosaurs, second 
only to Cymbospondylus petrinus (Middle Traissic, Nevada) in total body 

12 



STAGES 


ZONES 


LITHOLOGICAL 
FORMATIONS 


LOCALITIES 


UPPER 
URIAN 


Ech/oceras raricostatum 


Black Marl of 
Black Ven 


Lyme Regis 
Dorset 


Oxynoticeras oxynotum 


Asteroceras obtusum 


LOWER 
SINEM 


Caenisites turneri 


Shales-with-Beef" 


Arnioceras semicostatum 


Blue Lias 


Arietites bucklandi 


z 
< 

o 

z 

LU 

X 


Schlotheimia angulata 


Alsatites llasicus 






Psiloceras planorobis 




Street 
Somerset 



Fig. 5 The ammonite zones of the English Lower Lias (based upon Dean et ai, 1961), 



length. C. petrinus has been estimated to reach 10 metres (McGowan, 
1972b), whereas T. platyodon probably did not exceed 9 metres (data from 
BMNH R1155 and bmnh 2003). 

SKULL 

Snout relatively long and straight, tapering gently to the tip. Ratio, length 
of snout to length of jaw 0.64 in neotype, observed range 0.62-0.64 
(n = 3). Maxilla long and robust, makes substantial contribution to mar- 
gin of upper jaw; ratio, length of premaxillary segment to length of jaw 
0.34 in neotype, observed range 0.30-0.34 (n = 2). As noted elsewhere 
(McGowan, 1972a), possession of a relatively long maxilla is a primitive 
character. 

Orbit relatively small; ratio, diameter of orbit to length of jaw 0.16 in 
the neotype, observed range 0.16-0.17 (n = 3). Sclerotic aperture also 
relatively small; ratio, internal diameter of sclerotic ring to diameter of 
orbit (indeterminate in neotype) 0.32 in rom 7972, 0.31 in bmnh R1158 
and 0.24 in bmnh R215. Possession of small orbital and sclerotic diam- 
eters are both primitive characters (McGowan, 1972a). External naris 
large; ratio, length of external naris to diameter of orbit, probably always 
exceeding 0.50, is 0.53 in rom 7972, 0.63 in bmnh R1158 and bmnh 
R1155, and 0.72 in bmnh R215. Ratio, length of prenarial segment to 
length of jaw 0.50 in neotype, range 0.46-0.50 (n = 3). Naris bilobed 
in BMNH R1158 (Fig. 6b), but not bilobed in either rom 7972 or bmnh 
14564 and not therefore a constant character. External lateral surfaces of 
tips of premaxillae marked in neotype (Fig. 6a) by fairly deep longitudinal 
striations, which converge anterodorsally giving serrated medial margin. 

13 



A 



^;a*'. 



"^ • .I*; .• 'i* • .•• * • v» / •. 5 . /if •., .^^ . •>< 1. •. \ . *: - op- . • • . 









^^^«^s«r>^ 



* liJ-l.^'; :':/•): 





■>....*'-^ 



pr-'". ''''^ .'■•* -'^ 5'**■g^•^-'•'•''li**»^4;■ 




Fig. 6 Temnodontosaurus platyodon (Conybeare), scale = 5 cm. 

A. BMNH 2003, tip of snout, dorsal view, showing striations. 

B. BMNH R1158, external naris, lateral view, showing bilobed appearance. 

14 



Because extreme tip of snout frequently lost in other specimens, it is not 
known if this is a diagnostic character. Internasal foramen (McGowan, 
1973b) present in neotype, bmnh R1 155, bmnh R215, and ROM 7972, but 
absent in bmnh R1158 and indeterminate in remaining specimens; may be 
considered a constant character. 

Probably also to be referred to T. platyodon are bmnh 2149 (and bmnh 
2150), a basioccipital and basisphenoid with associated atlas and axis, and 
bmnh 481, a partial vertebral column. Both specimens are from the Lower 
Lias of Lyme Regis, and are large (dorso-ventral height of centra 18.5 cm, 
width of basisphenoid 24.7 cm). It is noteworthy that the basioccipital is 
not drawn out into a peg anteriorly, as in latipinnates (McGowan, 1973b) 
but has a flat anterior face. A similar basioccipital condition occurs in the 
Cretaceous longipinnate Platypterygius americanus (uw 2421), and in an 
undescribed longipinnate skull from the Upper Jurassic of Norfolk (sMC 
J68516). It is suggested that the absence of a basioccipital peg may be a 
longipinnate character. 

FINS 

Whereas the skull of T. platyodon is adequately known, knowledge of fin 
structure is incomplete because of scarcity of associated skeletons. Fore- 
and hindfins both preserved in neotype, but close inspection reveals right 
forefin is entirely plaster, and last two (distal) horizontal rows of left hind- 
fin are plaster also. From level six onwards (radius and ulna are designated 
level one, radiale, intermedium and ulnare level two, and so on; see 
"Materials and Methods") elements of left forefin well spaced, giving sus- 
piciously unnatural appearance. However, all elements are embedded in 
matrix (which has been painted) and there is even a small depression 
indicating where an element has been lost (distal to level 8); left forefin 
therefore genuine. Bones of two hindfins similarly embedded in matrix and 
likewise reliable. 

In neotype hindfin approaches size of forefin; ratio, forefin length to hind- 
fin length 1 .4 (mean value 2.5 in Stenopterygius quadriscissus). Both fins long 
and narrow; aspect ratio (maximum length/maximum width) of left forefin 
3.4 (mean value 2.3 in S. quadriscissus). Aspect ratio of left and right 
hindfins 2.6 and 2.2 respectively (mean value 2.1 in S. quadriscissus). 
Three primary digits in neotype forefin with evidence of a pre-axial 
accessory digit commencing at level eight; as this consists of only two 
elements it can be ignored. Maximum number of elements in the longest digit 
16. Notching in first three pre-axial elements. Forefins incomplete in bmnh 
R2918 but have three primary digits, one post-axial accessory. Longest 
digit has 12 elements, but incomplete. In OUM J29170 right forefin more 
complete than left, has three primary and one accessory digits. Maximum 
number of elements in longest digit 14; radius and radiale notched. 

In conclusion, the forefin has three primary digits and one post-axial 
accessory digit, the maximum number of elements in the longest digit 
probably does not exceed 18, and the radius and radiale are notched. The 
hindfin (in the neotype) has three primary and one post-axial accessory 

15 



A 



B 





Ant n 



Fig. 7 A comparison of the pectoral girdle of bmnh 2003 and bmnh 14564 (after 
Owen, 1881). 
CI, clavicle; Co, coracoid; H, humerus; Sc, scapula; Ant n, anterior notch. 

A. BMNH 2003, Lower Lias, Lyme Regis (pi. 31, fig. 3). [/. platyodon] 

B. BMNH 14564, Lower Lias, Lyme Regis (pi. 31, fig. 4). [/. lonchiodon] 



digits, and the maximum number of elements in the longest digit is 12. The 
forefin is only marginally longer than the hind, and has a high aspect ratio. 

AXIAL SKELETON AND GIRDLES 

Vertebral count from atlas to pelvic girdle 46 or 47 in neotype, estimated 
46 in BMNH R2918, and 46 or 47 in bmnh 14564. Only in bmnh R2918 
is vertebral column sufficiently well preserved for a vertebral count to the 
tail bend, estimated at 86 or 87 (mean counts to pelvic girdle and tail 
bend 47 and 83 respectively in S. quadriscissus, and 44 and 77 in the 
latipinnate Ichthyosaurus communis) . Pre-flexural body segment relatively 
longer in T. platyodon than S. quadriscissus (see McGowan, 1972b, Fig. 
17); T. platyodon was a longer-bodied animal. Individual vertebral centra 
with typical ichthyosaurian disc shape; in neotype (jaw length 148 cm) 
diameter of dorsal centra 11.5 cm, in OUM J29170 (jaw length 169 cm), 
dorsal centra 14.5 cm. In longest skull recorded, bmnh R1155 (jaw length 
approximately 221 cm), cervical centra 13.5 cm diameter compared with 
18.5 cm in partial vertebral column bmnh 48 1 . It is therefore concluded that 
the length of the jaw may have exceeded 221 cm. The limb girdles are in- 
variably indeterminate in ichthyosaurs, and thus of reduced systematic inter- 
est, but it may be noted that they are relatively large and robust in T. platy- 
odon. The coracoid apparently has only an anterior notch (Fig. 7b: Ant n). 

DENTITION 

Teeth are of little value in ichthyosaur classification (McGowan, 1969) 
and it is interesting to note that Conybeare's flattened ''platyodon tooth'' 
(Conybeare, 1822, pi. 15, fig. 7) is absent from all specimens thus far 



16 



referred to the species T. platyodon (and for that matter from other 
ichthyosaurs examined). Teeth are clearly visible in the neotype (bmnh 
2003), BMNH R1158, BMNH R215, and ROM 7972 and all are round in 
cross-section. 

Remarks 

Figures were not given by Owen in his description of /. lonchiodon, but 
reference was made to a specimen 15 feet (4.5 metres) long in the British 
Museum (bmnh 14564) purchased from T. Hawkins and figured in a 
subsequent paper (Owen, 1881, pi. 31, figs. 4-7). In his original descrip- 
tion Owen compared /. lonchiodon with /. platyodon noting the following 
differences: head of /. lonchiodon relatively longer, lower jaw deeper and 
tapering more rapidly to tip, teeth more slender with circular cross-section, 
vertebral centra wider antero-posteriorly, scapula with deeper posterior 
concavity, forefin relatively smaller and fore-and hindfins do not approach 
similar size as they do in /. platyodon. Owen referred bmnh 2003 and 
BMNH R1158 to /. platyodon (1881, pi. 31, figs. 1 and 2 respectively), 
but if these specimens are compared with the holotype of /. lonchiodon 
(bmnh 14564) they are found to be indistinguishable on Owen's diag- 
nostic characters: 





BMNH 2003 


BMNHR1158 


BMNH 14564 


Length of skull 
Length of body 


0.28 





0.28 


Depth of jaw 




0.10 


0.10 


Length of jaw 








Shape of tooth section 


Round 


Round 


— 


Width of centrum 


0.40 




0.38 



Height of centrum (30th centrum) 

Furthermore, if the scapula of bmnh 2003 is compared with that of bmnh 
14564 (Owen, 1881, pi. 31, figs. 3-4), it is seen that while they differ some- 
what in shape, the posterior concavity is no deeper in bmnh 2003 (Fig. 7). 
The species /. lonchiodon Owen is thus concluded to be a junior synonym 
for T. platyodon (Conybeare). 



Temnodontosaurus risor sp. nov. 

Fig. 8 



Etymology 

Risor, Latin (masc), a mocker 

Ichthyosaurus communis Conybeare, Owen (pro-parte), 1840, p. 108. 
Ichthyosaurus communis Conybeare, Lydekker (pro-parte), 1889a, p. 41, 
fig. 21. 

17 



A 





B 



C 




J 



Fig. 8 



18 



Temnodontosauriis risor sp. nov., scale = 25 cm. 

A. BMNH 43971, holotype, Lower Lias, Lyme Regis. 

B. SMC J68446, Lower Lias, Lyme Regis. 
c. BMNH R3 11, Lower Lias, Lyme Regis. 



Diagnosis 

Medium sized ichthyosaurs, length of jaw ^ 100 cm; snout distinctly re- 
curved, ratio, length of snout to length of jaw > 0.57 but probably not 
exceeding 0.62; skull and lower jaw with recurved profile; orbit relatively 
large, ratio, diameter of orbit to length of jaw ^ 0.18; sclerotic aperture 
relatively small, ratio, internal diameter of sclerotic ring to diameter of 
orbit < 0.35; maxilla of moderate length, ratio, length of premaxillary 
segment to length of jaw > 0.36; ratio, length of prenarial segment to 
length of jaw > 0.42; maxillary tooth count > 15. Lower Liassic in age 
[Upper Hettangian to Lower Sinemurian]; largely, if not wholly, confined 
to Lyme Regis, Dorsetshire. 

Holotype 

BMNH 43971, a complete skull in the British Museum (Natural History). 

Other Material 

SMC J68446 (complete skull) ; bmnh R3 11 (partial skull) . 

Locality and Horizon 

All material thus far referred to this species is from the Lower Lias of 
Lyme Regis, Dorset. The geological range is taken to be from the zone of 
Schlotheimia angulata to that of Arnioceras semicostatum (see Fig. 5) 
[Upper Hettangian to Lower Sinemurian]. 

Description 

The present species is known only from cranial material. The holotype, 
a well preserved laterally compressed skull, exposed on the right, has a 
jaw length of 70 cm, and is the smallest of the three referred specimens; 
BMNH R311, the largest, has a jaw length of 83 cm. Characteristic of the 
species is the recurved snout which imparts the sardonic expression re- 
flected in the trivial name. Ratio, length of snout to length of jaw 0.59 in 
holotype, observed range 0.59-0.62 (n = 3), (0.62-0.64 in T. platy- 
odon, n = 3 ) . Orbit relatively large, ratio, diameter of orbit to length of 
jaw 0.20 in the holotype, observed range 0.19-0.20 (n= 3), (0.16- 
0.17 in T. platyodon, n = 3). Sclerotic ring well preserved only in holo- 
type; ratio, internal diameter of sclerotic ring to diameter of orbit 0.26 
(0.24-0.31 in T. platyodon, n = 4). Relative small size of maxilla re- 
flected in large value of ratio, length of premaxillary segment to length of 
jaw, 0.39 in holotype, range 0.38-0.39 (n = 3), (0.30-0.34 in T. 
platyodon, n = 2). Because of distortion external naris in holotype difficult 
to delimit; in bmnh R31 1 it is relatively small, ratio, length of external naris 
to diameter of orbit 0.44 (0.53-0.72 in T. platyodon, n = 4). Ratio, 
length of prenarial segment to length of jaw 0.44 in holotype, observed 
range 0.44-0.49 (n = 3), (0.46-0.50 in T. platyodon, n = 3). 

Remarks 

T. risor is most closely related to T. platyodon, but is a much smaller 
species (observed size ranges, based on jaw length, 70-83 cm and 135- 

19 



T. lisor 


/. communis 


<0.21 


>0.21 


<0.35 


> 0.35 


<0.40 


>0.40 



221 cm respectively). In marked contrast to T. platyodon, the snout of 
T. risor has a curved profile and also appears to be relatively shorter. In 
possessing a relatively larger orbit and smaller maxilla than T, platyodon, 
T. risor represents a more advanced stage of cranial evolution (for a dis- 
cussion of evolutionary trends see McGowan, 1972a and 1972b). 

The superficial resemblance to /. communis is due to their similar snout 
proportions; the mean value for the ratio, length of snout to length of jaw 
is 0.61 in T. risor and 0.63 in /. communis. The differences between the 
two species are fundamental: 

Diameter of orbit/length of jaw 

Internal diameter of sclerotic ring/diameter of orbit 

Length of premaxillary segment/length of jaw 

Furthermore, T. risor is a considerably larger species, having an observed 
size range of 70-83 cm (jaw length) whereas the largest recorded speci- 
men of /. communis has a jaw length of only 54 cm. 



Temnodontosaurus eurycephalus sp. nov. 

Fig. 9 

Etymology 

€vpv<j Gk. (masc.) wide; /ce^aXr; Gk. (fem.) head 

Ichthyosaurus breviceps Owen (pro-parte), 1881, p. 109, pi. 29, fig. 1. 
[non] Ichthyosaurus platyodon Conybeare, Lydekker, 1889a, p. 98. 
Eurypterygius breviceps (Owen), Von Huene, 1922, p. 8, pi. 1, fig. 3 
[referred to in the figure legend, in error, as Eurypterygius brevirostris 
(Owen)]. 

Diagnosis 

Large ichthyosaurs, adult jaw length exceeding 100 cm; snout relatively 
short, ratio, length of snout to length of jaw < 0.58; skull and lower jaw 
deep; orbit relatively small, ratio, diameter of orbit to length of jaw 

< 0.21; ratio, internal diameter of sclerotic ring to diameter of orbit 

< 0.35; maxilla relatively long, ratio, length of premaxillary segment to 
length of jaw < 0.36 and probably < 0.30; external naris relatively short, 
ratio, length of external naris to diameter of orbit <0.50; ratio, length of 
prenarial segment to length of jaw < 0.42; teeth relatively few in number, 
maxillary tooth count probably <15. Lower Liassic in age [Upper Het- 
tangian to Lower Sinemurian] and largely if not wholly confined to Lyme 
Regis, Dorsetshire. 

Holotype 

BMNH Rl 157, an isolated skull in the British Museum (Natural History). 

Other Material 

Nil 

20 




t 



J 



Fig. 9 Temnodontosaurus eiirycephalus sp. nov., bmnh R1157, holotype, Lower Lias, 
Lyme Regis, scale = 50 cm. 



Locality and Horizon 

The holotype, from the Lower Lias of Lyme Regis, was collected from a 
Umestone bed called Broad Ledge. Broad Ledge is probably synonymous 
with Grey Ledge (Woodward and Ussher, 1911, p. 37), being the top of 
a platform of rocks exposed at low tide some distance from the eastern 
jetty, southeast of Church Cliffs. The horizon corresponds with the zone 
of Arietites bucklandi and is lowermost Sinemurian (see Fig. 5). 



Description 

The holotype is a large laterally compressed skull, right side exposed. 
Length of lower jaw 111 cm, skull 102 cm. Snout much abbreviated, skull 
roof slopes quite steeply towards tip of snout. Ratio, length of snout to 
length of jaw 0.55 (0.62-0.64 in T. platyodon, n = 3). Skull and lower 
jaw both very deep dorsoventrally, giving head a robust appearance. Orbit 
and aperture of sclerotic ring both relatively small; ratio, diameter of orbit 
to length of jaw 0.18 (0.16-0.17 in T. platyodon, n = 3), ratio, internal 
diameter of sclerotic ring to diameter of orbit 0.29 (0.24-0.31 in T. 
platyodon, n = 4). Maxilla long and fairly stout, ratio, length of pre- 
maxillary segment to length of jaw only 0.27 (0.30-0.34 in T. platyodon, 
n = 2). External naris set well forward and relatively small; ratio, length 
of external naris to diameter of orbit 0.44 (0.53-0.72 in T. platyodon, 
n = 4); length of prenarial segment to length of jaw only 0.38 (0.46- 
0.50 in T. platyodon, n = 3). 

Dentition 

Teeth, large conical pegs with bulbous roots, few in number, and well 
spaced. The stout teeth, massive lower jaw, and broad rostrum are all 
indicative of an effective crushing apparatus. T. eurycephalus may have 

21 



preyed upon other ichthyosaurs : the bony element (basisphenoid) clenched 
between the teeth of bmnh R1157 may not be part of its own skull but that 
of some victim. 

Remarks 

BMNH R1157 was figured and described by Owen in 1881 and referred to the 
new species Ichthyosaurus breviceps, even though there was a considerable 
size disparity between this specimen (jaw length 111 cm) and the holotype of 
/. breviceps, bmnh 43006 (jaw length 25.3 cm). The only similarity between 
the two is in the extreme brevity of the snout; the ratio, length of snout to 
length of jaw is 0.55 in bmnh R1157 and in bmnh 43006. However, the 
orbit is much smaller in bmnh R1157, and the ratio, diameter of orbit to 
length of jaw is only 0.18 compared with 0.31 in bmnh 43006. This dis- 
crepancy cannot be reconciled in terms of relative growth because the 
growth of the orbit appears to have had a positive allometry in /. breviceps 
(McGowan, 1973a). The maxilla is relatively longer in bmnh R1157 than 
in BMNH 43006, with values for the ratio, length of premaxillary segment 
to length of jaw 0.27 and 0.44 respectively. Here again the disparity cannot 
be explained in terms of relative growth because the maxilla appears to 
have had a negative allometry in /. breviceps, larger individuals tending to 
have relatively smaller maxillae (McGowan, 1973a). Possession of small 
orbit, small sclerotic ring diameter and large maxilla are all longipinnate 
characters (McGowan, 1972a), and there can be no doubt that bmnh R1 157 
is a longipinnate. bmnh R1 157 cannot therefore be referred to the latipinnate 
species /. breviceps, and is accordingly described here as a new longipinnate 
species. 



Temnodontosaurus longirostris (Mantell) 

Fig. 10 

Ichthyosaurus longirostris Mantell, 1851, p. 385. 

[non] Ichthyosaurus longirostris Mantell, Jager, 1856, p. 951, pi. 30. 

Ichthyosaurus longirostris Mantell, Owen, 1881, p. 124, pi. 25, fig. 2; 

pi. 28, fig. 3;pl. 32, figs. 7, 8, 9. 

Ichthyosaurus latifrons Koenig, Lydekker, 1889a, pp. 89-92, figs. 31-32. 

Ichthyosaurus longirostris Mantell, Fraas, 1891, p. 63. 

Leptopterygius laitfrons (Koenig), Von Huene (pro-parte), 1922, p. 15, 

pl. 3, fig. 2. 

Emended Diagnosis 

An inadequately known species of moderate size, length of jaw probably 
not exceeding 100 cm; snout very long and thin, ratio, length of snout to 
length of jaw > 0.70; orbit relatively small, ratio, diameter of orbit to 
length of jaw probably ^ 0.18; sclerotic aperture relatively large for a 
longipinnate, but ratio, internal diameter of sclerotic ring to diameter of 
orbit probably always < 0.35; forefin long and narrow with three primary 
digits and one post-axial accessory digit; radius notched, perhaps also 

22 




Kr^.' 
















DO 



Fig. 10 Temnodontosaurus longirostris (Mantell), scale = 50 cm. 

A. BMNH 36182, Lower Lias, Barrow-on-Soar, Leicestershire, after Owen, 1881, 
pi. 32, fig. 7; B. sec 1, Lower Lias, Street, Somersetshire. 



23 



radiale and other elements in first digit; maximum number of elements in 
longest digit probably < 18. Liassic in age, probably ranging from Lower 
to Upper divisions. 

Holotype 

BMNH 14566, an incomplete skeleton (dorsal aspect exposed) apparently 
from the Upper Lias of Whitby, Yorkshire, figured in Owen, 1881, pi. 32, 
fig. 8. 

Referred Material 

BMNH 36182, an almost complete skeleton from the Lower Lias of 
Barrow-on-Soar; sec 1, the anterior portion of an imperfect skeleton com- 
prising partial skull, near-complete forefin, and an imperfect pectoral 
girdle, from the Lower Lias of Street, Somerset, bmnh R1120, a poorly 
preserved skeleton from the Lower Lias of Lyme Regis figured by Owen 
(1881, pi. 32, fig. 1) is also referred to the present species. 

Locality and Horizon 

According to Lydekker (1889a, p. 91) the holotype is from the Upper 
Lias of Whitby, Yorkshire, whereas the two referred specimens, bmnh 
36182 and sec 1 are both from the Lower Lias of Barrow-on-Soar, 
Leicestershire, and Street, Somerset, respectively. As far as I am aware, 
no Liassic species extends from Lower to Upper divisions, but this may 
be an artifact of the geological record, due to lack of good Upper Liassic 
exposures (ichthyosaurs with very extensive geological ranges are known 
from the Cretaceous, McGowan, 1972c). It could be that Lydekker was 
mistaken in referring bmnh 14566 to the Upper Lias of Whitby; the Lower 
Lias does outcrop in Whitby, but most if not all ichthyosaurs from Whitby 
have been collected from the Upper Lias. For the present the geological 
range of T. longirostris is taken to extend from Lower to Upper Lias. 

Most of the reptilian remains from Street have been collected from the 
''pvQ-planorbis Beds" (Arkell, 1933, p. 123) which are at the base of the 
Lower Lias [Lowermost Hettangian]. At Whitby ichthyosaurs have been 
collected from the zones of Hildoceras bifrons and Harpoceras falcifer 
(Hemingway et al., 1968) which are in the lower part of the Upper Lias 
[Lower Toarcian]. The geological range of T. longirostris is therefore taken 
to be from Lower Hettangian to Lower Toarcian. 

Emended Description 

Because of incomplete material, Tenmodontosaurus longirostris (Mantell) 
is only moderately well known. 

SKULL 

Snout long and thin, ratio, length of snout to length of jaw approximately 
0.79 in holotype, compared with 0.72-0.73 (n = 2) in the other English 
long-snouted species Ichthyosaurus tenuirostris (0.62 — 0.64 in T. platy- 
odon, n = 3). Orbit appears large but ratio, diameter of orbit to length 
of jaw only 0.16 in holotype and bmnh R1120, compared with 0.22 in 
/. tenuirostris (n = 1 ) and 0.16-0.17 in T. platyodon (n = 3). Sclerotic 

24 



aperture also relatively small, ratio, internal diameter of sclerotic ring to 
diameter of orbit 0.33 in holotype and sec 1, compared with 0.41 in /. 
tenuirostris (n= 1) and 0.24-0.31 in T. platyodon (n = 4). 

FINS 

Knowledge of the forefin is incomplete, but it is certainly longipinnate, with 
three primary digits and one post-axial accessory digit (Fig. 10). The best 
known forefin (sec 1 ) is almost complete and has a maximum number of 
16 elements in the longest digit, though one or two may be missing from 
the extreme tip. Only the radius is notched in sec 1 whereas in bmnh 36182 
and BMNH R1120 the radius, radiale, and third element of the first digit 
are emarginated. The hindfin of bmnh 36182 has three primary digits and 
several of the elements of the first digit are emarginated. 

Remarks 

The species /. longirostris is usually attributed to Owen, 1881 (Lydekker, 
1889a, p. 89; Woodward and Sherborn, 1890, p. 239; Kuhn, 1934, p. 55) 
and sometimes to Jager 1856 (Lydekker, 1889a, p. 89) but the first 
description of the species was given by Mantell in 1851, who wrote, 
"ICHTHYOSAURUS LONGIROSTRIS Wall-case E— In . . . Case E 
there is part of the skeleton of an Ichthyosaurus from Whitby, about six 
feet [1.8 m] in length. It is remarkable for the exceedingly slender and 
elongated muzzle; the skull is crushed; and with the exception of the chain 
of vertebrae which extends to the tail, and a few bones of one paddle, 
there are no characteristic parts preserved. The specific name, longirostris, 
is affixed to this specimen; but I cannot ascertain that it is figured or 
described." (Mantell, 1851, p. 385). Sufficient information is given to 
identify the specimen, the locality is recorded and, most important, note 
is taken of the extremely long snout. In my opinion this constitutes a vahd 
description. Lydekker (1889a, p. 91) identified Mantell's specimen as 
BMNH 14566, from the Upper Lias of Whitby, and gave a description 
which matches Mantell's description, noting that the dorsal aspect of the 
skull is figured by Owen (1881, pi. 32, fig. 8). Jager (1856, p. 951) did 
not consider that Mantell had adequately described the species and there- 
fore gave his own description which included the figure of a skull (Jager, 
1856, pi. 30). This skull, however, should probably be referred to the 
genus Eurhinosaurus. The skeleton figured by Fraas (1891, pi. 12, fig. 5) 
from the Upper Lias of Holzmaden might be referable to T. longirostris. 



25 



Systematic Summary 



The genus Temnodontosaurus, which is largely confined to the Lower Lias, 
contains four species, T. platyodon (Conybeare), T. longirostris (Man- 
tell), and the two new species T. risor and T. eurycephalus. 

Still to be considered is /. acutirostris Owen, from the Upper Lias of 
Whitby, Yorkshire. /. acutirostris and Stenopterygius quadriscissus (Quen- 
stedt) [Upper Lias, Germany] are found to be almost indistinguishable 
from each other but quite distinct from T. platyodon (Table 1). /. acuti- 
rostris is accordingly referred to the genus Stenopterygius. Because the 
present work is confined to English material it is not appropriate to give 
here an emended diagnosis of the family Stenopterygiidae, which is known 
largely from Germany. This will be the subject of another study (Mc- 
Gowan, in preparation). 



Table 1. Comparison of cranial and body characters between the longipinnate species 
S. acutirostris, S. quadriscissus and T. platyodon. 





.Bo 

1 

■Ct 


1 

1 






CO 


Co 


K 


'•Length of snout/length of jaw 


0.67 


0.67 


0.63 


*Diameter of orbit/length of jaw 


0.20 


0.20 


0.16 


* Length of premaxillary segment/ 








length of jaw 


0.46 


0.47 


0.34 


'•'Internal diameter of sclerotic ring/ 








diameter of orbit 


0.34 


0.38 


0.28 


"Length of prenarial segment/ 








length of jaw 


0.57 


0.56 


0.49 


'•■'Length of external naris/ 








diameter of orbit 


0.35 


0.39 


0.66 


Number of primary digits 


3 


3 


3 


Number of accessory digits 


1 or 2 


2 


1 


Maximum number of elements in 








longest digit 


16 


17 


14 


Maximum recorded size (jaw length, cm) 


153 


55 


221 



*Mean values 



26 



Family Stenopterygiidae Von Huene 1948 
Genus Stenopterygius Jaekel 1904 



Stenopterygius acutirostris (Owen) 

Fig. 1 1 

Ichthyosaurus acutirostris Owen, 1840, p. 121. 

Ichthyosaurus longipennis Mantell, 1851, p. 378. 

Ichthyosaurus acutirostris Owen, Phillips, 1875, p. 272. 

Ichthyosaurus acutirostris Owen, Blake, 1876, p. 253. 

Ichthyosaurus crassimanus Blake, 1876, p. 253, pi. 1, fig. 9. 

Ichthyosaurus zetlandicus Seeley, 1880, pp. 635-646, pi. 25. 

Ichthyosaurus acutirostris Owen, Owen, 1881, p. 121, pi. 28, fig. 2. 

Ichthyosaurus longifrons Owen, 1881, p. 118, pi. 23, figs. 1-5; pi. 24, 

fig. 1 ; pi. 25, fig. 1 ; pi. 26, fig. 1 ; pi. 27, figs. 2-5. 

Ichthyosaurus acutirostris Owen, Lydekker, 1889a, p. 73. 

Leptopterygius acutirostris Owen, Von Huene (pro-parte), 1922, p. 25. 

[non] Ichthyosaurus (cf.) acutirostris Owen, Lydekker, 1889a, p. 74, fig. 

27. 

[non] Ichthyosaurus acutirostris Owen, Fraas, 1891, pi. 8; pi. 11, fig. 1. 

[non] Leptopterygius acutirostris (Owen), Hauff, 1953, pi. 19. 

Emended Diagnosis 

Large ichthyosaurs, length of jaw > 60 cm in mature individuals, fre- 
quently > 100 cm; snout relatively long, ratio, length of snout to length 
of jaw ^ 0.62; snout tends to taper to a sharp point; orbit often relatively 
large, ratio, diameter of orbit to length of jaw usually not less than 0.18 
and may exceed 0.20; sclerotic aperture relatively large, ratio, internal 
diameter of sclerotic ring to diameter of orbit frequendy > 0.35; maxilla 
relatively short, ratio, length of premaxillary segment to length of jaw 
> 0.36; ratio, length of external naris to diameter of orbit < 0.60; forefin 
with three primary digits and one or two accessory digits; head large 
relative to body, especially in larger individuals. Jaw and body length data 
approximate more closely to equation, jaw length = 0.1 X (body length) ^-^ 
than to the equation, jaw length = 3.363 X (body length )^"'*^" (see remarks 
below). Upper Liassic in age, apparently confined to England, probably to 
the Whitby locality of Yorkshire. 

Holotype 

BMNH 14553 (Lydekker, 1889a, p. 73). There is some doubt regarding 
the present whereabouts of this specimen (Walker, pers. comm.), and only 
an extensive search of the British Museum would confirm whether it has 
been lost. At present this is not practical and it will therefore be recorded 
that the holotype may be lost. 



27 





Q 



Fig. 1 1 Stenopterygius acutirostris (Owen), scale = 40 cm. 

A. WMY 5, Upper Lias, Lofthouse, Yorkshire. 

B. WMY 876S, Upper Lias, Kettleness, Yorkshire (photograph laterally inverted), 
c. WMY 877S, skull, Upper Lias, Whitby, Yorkshire (photograph laterally in- 
verted). 

D. BMNH 14533, skull of holotype, Upper Lias, Whitby, Yorkshire (after Owen, 
1881,pl. 28,fig. 2). 



28 



Other Material 

WMY 5, WMY 2546S, WMY 876S, wmy 878S, ym 497 (complete or near 
complete skeletons); wmy 877S (skull with some post-cranials); wmy 
876S(H1), BMNH 1500a (complete skulls) and smc J35176 (partial skull). 

Locality and Horizon 

All the material referred to this species is from the Upper Lias, in the 
vicinity of Whitby, Yorkshire. Most of the specimens were collected from 
the Alum Shales, and also from the Hard Shales and Bituminous Shales 
lying above the Jet Rock (see Arkell, 1933, p. 182; Wilson, 1948, p. 28) 
in the ammonite zone of Hildoceras bijrons and Dactylioceras commune 
[Lower Toarcian]. 

Emended Description 

Because of poor preservation the species is not adequately known, even 
though it is represented by at least ten specimens. The holotype is appar- 
ently not well preserved. 

SKULL 

The type skull, figured by Owen (1881, pi. 28, fig. 2) is reproduced in 
Fig. llD (Lydekker, 1889a, p. 74, erroneously refers to Owen's figure as 
pi. 32, fig. 8). Snout frequently sharply pointed, as in wmy 876S, bmnh 
1500a, WMY 876S(H1) and wmy 878S, but decurved appearance figured 
by Owen, seen clearly in wmy 876S, probably an artifact of preservation 
because it is not a constant feature. Decurved snouts in bmnh 1500a and 
WMY 876S(H1) almost certainly due to dorso-ventral compression, the 
thin snout being readily distorted. Snout quite straight in wmy 876S 
and WMY 877S, even slighdy recurved in wmy 5. Ratio, length of snout 
to length of jaw 0.62-0.68 (n = 6), mean value 0.66 (0.62-0.64 in 
T. platyodon, n = 3 ) . Measurements taken from Owen's figure of type 
skull give a value of 0.78 for this ratio, but this may be because the snout 
was exaggerated in his figure. 

Maxilla relatively shorter than in the Temnodontosaurus, indicating a 
more advanced stage of cranial evolution (McGowan, 1972b); ratio, 
length of premaxillary segment to length of jaw 0.40-0.42 (n = 2), 
mean 0.41 (0.30-0.34 in T. platyodon, mean 0.32, n = 2). Orbital con- 
dition similarly more advanced than Temnodontosaurus, ratio, diameter 
of orbit to length of jaw 0.16-0.23 (n = 4), mean 0.20 (0.16-0.17 in 
T. platyodon, mean 0.17, n = 3). Sclerotic aperture variable, ratio, internal 
diameter of sclerotic ring to diameter of orbit 0.28-0.40 (n = 4) compared 
with 0.24-0.31 (n = 4) in T. platyodon. Ratio, length of external naris 
to diameter of orbit (not always a reliable character) relatively small, 
0.31-0.57 (n = 4), mean 0.42, compared with 0.53-0.72 mean 0.63 
(n = 4) in T. platyodon. Internasal foramen absent (because of poor 
preservation this can only be determined in one specimen, smc J35176, 
the holotype of Seeley's /. zetlandicus) . 



29 



FINS 

Fins generally poorly preserved, but are determinate in ym 497, wmy 5, 
WMY 877S, WMY 2546S and apparently in holotype. Three primary and 
one accessory digits, except in wmy 2546S, which also has one pre-axial 
accessory digit. Maximum number of elements in longest digit an estimated 
14 in WMY 5, 16 in wmy 2546S and 19 or 20 in ym 497. Notching in 
radius, radiale and third element in wmy 5, in radius and radiale in wmy 
2546S, only in radius in ym 497, with no notching in wmy 877S. Forefin 
not as long and narrow as in T. platyodon, aspect ratio only 2.6 (n = 3) 
compared with 3.1 in T. platyodon and 2.3 in S. quadriscissus (mean 
values). Relative lengths of fore- and hindfins variable, ratio, length of 
forefin to length of hindfin 2.2 in ym 497, 1.2 in wmy 2546S (2.5 in S. 
quadriscissus, 1.4 in neotype of T. platyodon) . 

In WMY 2546S left fore- and hindfins are composites with individual 
elements set in plaster in a latipinnate configuration (four primary digits). 
Fins on the right side appear authentic and have a longipinnate configura- 
tion with three primary digits. Of interest in wmy 5 is that the humerus has 
three distal facets (comparable with Platypterygius, see McGowan, 1972c; 
and Ophthalmosaurus, see Andrews, 1910), the smaller of these probably 
being for the pisiform. It is not known whether this is a constant feature 
of the species. To summarize, the forefin has three primary digits with one 
post-axial accessory digit and sometimes one pre-axial accessory. Maxi- 
mum number of elements in longest digit up to 20. Notching usually 
present. 

AXIAL SKELETON AND GIRDLES 

Vertebral count to pelvic girdle between 48 and 50 in wmy 2546S, and 
approximately 48 in wmy 876S. Vertebral count to tail bend difficult to 
determine; in wmy 2546S there is some indication of a disturbance at level 
77 and another at level 93, either of which could indicate the position of 
the tail bend. In wmy 876S there is some indication of the bend at about 
level 76. It is tentatively concluded that the vertebral count to the tail 
bend is approximately 76. 

Partial pectoral girdles preserved in wmy 878S and wmy 5 but comprise 
Httle more than the coracoids. The coracoids are fairly thick and robust and 
the pectoral girdle may have been well developed. Anterior notch present. 

DENTITION 

The teeth are of the usual ichthyosaurian form but appear to be relatively 
small (well marked in SMC J35176). 

Remarks 

1. Reasons for considering S. acutirostris to be distinct from 
S. quadriscissus 

The only difference between S. acutirostris and S. quadriscissus is size, the 
former reaching about three times the size of the latter (based on jaw 
length), and it seemed reasonable to conclude that they were part of a 

30 



continuous growth series of one and the same species. However, the larger 
individuals have relatively larger heads than the smaller ones, contrary to 
the usual ontogenetic pattern. Allometric growth constants have recently 
been evaluated for S. quadriscissus (McGowan, 1973a) and the relation- 
ship between the growth of the head relative to the body has been found 
to conform to the equation y = 3.363x^-^^^ (from the allometric growth 
equation y = bx" where y = organ size, x = body size, a = the allo- 
metric growth constant and b = a second constant). In S. acutirostris, 
head growth relative to that of the body conforms to the equation y = 
0.1x^-2 but the small sample size (n = 4) does not permit confidence limits 
tQ be set for the estimates of a and b. 

Three possible conclusions may be drawn from this: 

A. S. quadriscissus and S. acutirostris represent males and females of a 
sexually dimorphic species. 

B. S. quadriscissus and S. acutirostris belong to a single species in which 
changes in allometric growth constants a and b occur during ontogeny. 

c. S. quadriscissus and S. acutirostris are distinct species differing in allo- 
metric growth constants and maximum attainable sizes. 

S. quadriscissus and S. acutirostris occur in separate localities (in Ger- 
many and England respectively), which may not be strictly contempora- 
neous. Sexual dimorphism may therefore be dismissed. 

Abrupt changes in allometric growth constants are uncommon in 
ichthyosaurs (McGowan, 1973a), but occur in other animals, usually asso- 
ciated with metamorphosis. Martin (1949) found growth in fishes to be 
characterized by a series of five stanzas corresponding to four larval stages 
and the sexually mature adult. Each stanza had a different set of values 
for a and b. In Rana temporaria, the allometric growth constant of the 
eye undergoes an abrupt change at metamorphosis (De Jongh, 1967), and 
Brown and Davies (1972) working on the cockroach Ectobius, found the 
majority of changes in growth constants coincided with metamorphic 
changes. 

If S. quadriscissus and S. acutirostris were part of a continuous growth 
series the abrupt change in allometric growth constants could not be cor- 
related with sexual maturity because pregnant females occur in the smaller 
form (S. quadriscissus). Maternal specimens are relatively small; 6293 
(Stuttgart Museum) has a body length of only 219 cm (See Fraas, 1891, 
p. 52, pi. 4, fig. 2) compared with 628 cm in the largest specimen of S. 
acutirostris (wmy 2546S). If the two species were part of the same growth 
series it would suggest attainment of sexual maturity at an early stage of 
growth. 

Acquisition of more extensive data from Germany could possibly alter the 
position, but for the present it is concluded that S. quadriscissus and S. 
acutirostris are separate species. 

2. Reasons for synonymizing /. crassimanus, I. longifrons and 
/. zetlandicus with S. acutirostris 

Blake's (1876, p. 253) description of /. crassimanus was mainly based on 
a large specimen in the York Museum which was redescribed in greater 

31 



detail by Melmore in 1930. The specimen (ym 497), collected from the 
Alum Shales north of Whitby, is unfortunately incomplete so that few 
measurements can be taken. The anterior portion of the snout is missing 
and is reconstructed in plaster, and the body is incomplete beyond the tail 
bend. If allowances are made for these missing parts, the head and body 
proportions approximate to the growth equation evaluated above for S. 
acutirostris. The forefin has three primary and one post-axial accessory 
digits, and is consistent with S. acutirostris. The only inconsistency is in the 
relative proportions of fore- and hindfins; in wmy 2546S {S. acutirostris) 
the ratios, forefin length to hindfin length and forefin width to hindfin width 
have values of 1.2 and 1.3, whereas in ym 497, the values are 2.2 and 1.6 
respectively. However, the relative size of fore- and hindfin is a variable 
character; for example in a sample of 10 specimens of S. quadriscissus the 
ratio, forefin length to hindfin length has a range of 2.2-3.1. The aspect 
ratio of the forefin is 2.4 in wmy 2546S and 2.9 in ym 497. It is therefore 
concluded that there are no major inconsistencies between ym 497 and wmy 
2546S and since ym 497 is from the same locality and horizon as S. acuti- 
rostris it is referred to that species. /. crassimanus Blake is thus a junior 
synpnym for 5. acutirostris. 

In describing /. zetlandicus Seeley wrote, 'T am acquainted with no other 
ichthyosaur in which the skull attains this broad, triangular form, with the 
orbits so far apart from each other and so moderately inclined, and with the 
nares so far in front of the orbits and relatively so large . . . These characters 
sufficiently distinguish the species from all others." (Seeley, 1880, p. 646). 
The holotype (smc J35176), a large incomplete skull from the Upper Lias 
of Whitby, is preserved in-the-round and the absence of distortion gives a 
very broad appearance when viewed from above. However, compared with 
other in-the-round skulls (bmnh R8177, bmnh 49203, both /. communis), 
SMC J35176 is no broader nor are the orbits any further apart. Because the 
skull is incomplete few comparisons can be made, but the ratio, length of 
external naris to the diameter of orbit is larger (0.57) than it is in S. acuti- 
rostris. However, the sample size is small (n = 3), and this character is known 
to be variable (for example in Stenopterygius quadriscissus the observed 
range is 0.25-0.45, n = 9). Furthermore the holotype of /. zetlandicus is 
from the same locality and horizon as S. acutirostris. I. zetlandicus is there- 
fore concluded to be a junior synonym for S. acutirostris. 

Owen's description of /. longifrons comprised a brief reference to some 
figures (1881, pis. 23-27). The skull figured is identified by Lydekker as 
BMNH 33157, from the Upper Lias of Curcy (1889a, p. 78). Lydekker noted 
that, "In all essential characters this specimen agrees with the preceding [a 
cast of the holotype of /. zetlandicus] ..." Lydekker synonymised /. longi- 
frons with (the now invalid) /. zetlandicus, a course taken by most authors 
(see Woodward and Sherborn, 1890). Only one character can be measured 
in BMNH 33157, the ratio, length of external naris to diameter of orbit (0.38) 
which lies within the observed ranges for 5". acutirostris (0.31-0.57). 
/. longifrons is thus concluded to be a junior synonym of S. acutirostris. 



32 



3. Reasons for rejecting /. latifrons Koenig as a nomen dubium 

I. latifrons was first mentioned by Koenig who figured an incomplete skull 
and partial vertebral column (1825, pi. 19, fig. 250) and most authorities 
consider this sufficient to make the name available (Woodward and Sher- 
born, 1890; Lydekker, 1889a, Kuhn, 1934). The figure was not accom- 
panied by a written description, and the specimen (bmnh R1122) is quite 
indeterminate. Owen figured the skull (1881, pi. 27, fig. 1) and Lydekker 
noted that it was probably collected from the Lower Lias of Barrow-on-Soar, 
Leicestershire (1889a, p. 90, fig. 33). Because the holotype is indeterminate 
it is not possible to compare it with any other material. The name /. latifrons 
is thus not applicable to any known taxon and is accordingly rejected as a 
nomen dubium. 



33 



Conclusion 

Of the five species of longipinnate ichthyosaurs of the English Lower Jurassic 
three are from the Lower Lias: Temnodontosaurus platyodon (Conybeare), 
T. risor, sp. nov., and T. eurycephalus, sp. nov. T. longirostris (Mantell) 
extends from Lower to Upper Lias, while Stenopterygius acutirostris (Owen) 
is confined to the Upper Lias. T. platyodon and S. acutirostris are both large, 
the former reaching a total length of 9 m, the latter approaching 8 m. Body 
length cannot be estimated for T. eurycephalus, but as the skull is in excess 
of 1 m, the species is assumed to have been comparable in size to T. platyodon 
and S. acutirostris. T. risor and T. longirostris were probably both of more 
moderate size, and much smaller than either T. platyodon or S. acutirostris. 

T. eurycephalus, with its short snout and massive skull, and T. longi- 
rostris, with its long and delicate snout were the most highly specialized 
species. It was suggested above that T. eurycephalus may have fed upon other 
ichthyosaurs, and the short deep skull and heavy teeth are certainly sug- 
gestive of a voracious predator. On the other hand, T. longirostris, with its 
long thin snout, probably fed exclusively on small fishes. 

S. acutirostris differs from its German contemporary S. quadriscissus in 
being larger and having a relatively larger head. Indeed the two species are 
so similar that they might well have evolved from similar stocks by way of a 
change in the allometric growth constants of the head and body. 



Acknowledgments 

I wish to express my sincere thanks for the help and hospitality I received 
from the staffs of the many institutions visited. I particularly wish to thank 
Dr. Alan Charig, Mr. Cyril Walker, Mr. Phillip Palmer, and Miss A. L. 
Holloway of the British Museum (Natural History) ; Dr. Colin Forbes of the 
Sedgwick Museum and Mr. Peter Biddlestone, formerly of the Sedgwick 
Museum, Cambridge, now of the Royal Ontario Museum; Mr. Phillip Powell 
of the Oxford University Museum; Mr. Allen Butterworth and Ms. Barbara 
Pyrah of the Yorkshire Museum; Mr. J. G. Graham of the Whitby Museum, 
Yorkshire; Dr. J. E. Hemingway of the University of Newcasde-upon-Tyne; 
Dr. Paul McGrew of the University of Wyoming; Mr. Andrew Mathieson 
and Mr. M. J. Jones of the Leicester County Museum, and the staff of the 
Clarks Shoe Museum, Street, Somerset. 

I thank Mrs. Janet Clarke and Mrs. Lynda Spicer, ROM, for their secre- 
tarial help; Mrs. Sophie Poray, rom, for the drawings; Mr. Leighton Warren 
and Mr. Alan McColl, Photography Department, rom, for photographs; 
and Miss E. Dowie of the rom library for assistance with literature searches. 
For reading the manuscript and making many helpful suggestions I thank 
Dr. Allan Baker, Department of Ornithology, rom and Dr. Gordon Edmund, 
Department of Palaeontology, rom. 

34 



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37